1. Technical Field
The present invention relates in general to mechanical fasteners, and in particular, to a mechanism for positioning an electronic assembly within a housing, such as, for example, a printed circuit board within an electronic chassis.
2. Background
Printed circuit boards (PCB) are used in many electronic devices, such as telecommunications equipment. In these devices, PCBs are often electrically connected to a back-plane using connectors that extend from the printed circuit card and that mate with connectors located on the backplane.
Generally, mechanical systems used for insertion and extraction of PCBs comprise a handle secured to the front end of the PCB or a pair of cam levers that cooperate with the front end of the chassis and slotted rail guides dedicated to each PCB mounted in an electronic chassis assembly.
Insertion and extraction handles present the advantage of being very simple. However, the disadvantage of these systems is that they are not usable with connectors requiring a high insertion and retention force to overcome mechanical resistance to properly mate the connector.
For this type of connector, a cam lever based mechanism is better suited. Some cam lever systems further comprise a snap latch system that cooperate with a mechanical part secured to the PCB to insure an automatic latching of the PCB in the chassis. The two following patents illustrate some prior art solutions.
U.S. Pat. No. 4,233,646 from Leung discloses an improved latching lever for use with a PCB. The latching mechanism comprises a hooked portion flexibly connected to the body portion of the latching lever, an actuating member solidly connected to the hooked portion for moving the hooked portion relative to the body portion, and a stop portion, solidly connected to the body portion for limiting the movement of the actuating member. A stud carried by the PCB is engaged by the hooked portion of the lever to enable the lever to latch. Moving the actuating member to contact the stop portion disengages the hooked portion from the stud, thereby unlatching the lever, and leaving the lever free to pivot about its pivot point.
In commonly assigned U.S. Pat. No. 6,058,579, a snap latch insertion and removal lever is described. The snap latch device has a handle with a pair of cam members extending from a lower end. The device also has a flexible snap which protrudes from the handle. The front end of the snap has a barbed lip. The device is designed to interlock a shuttle assembly to a stationary chassis. The device is pivotally mounted to the shuttle which carries a board with connectors. The device is movable between an engaged position and a retracted position. In the engaged position, the cam members engage an end wall on the chassis and the snap inserts through and engages a hole in the shuttle. The mechanical interlock between the cam members and the end wall rigidly secures the shuttle in the chassis. The device is moved to the retracted position by pulling back on the snap to dislodge the barbed lip. This release allows the device to rotate so that the cam members disengage the end wall. After the snap and cam members are clear of the hole and end wall, respectively, the shuttle may be completely removed from the chassis. The shuttle may be inserted and locked into the chassis by reversing these steps. The snap provides visual and audible feedback to the installer to insure a proper connection between the mating connectors on the shuttle and chassis.
One drawback of prior art designs is that the force required to mate the PCB is applied on the front end of the card while connectors are located on the back end. This results in undesired flexing of the PCB during insertion, thereby decreasing its reliability and utility by creating a heightened risk of micro cracks within the internal signal layers of the PCB.